1. Field of the Invention
The present invention relates generally to seat belt buckles having an electrical switch therein to detect insertion of a tongue plate into a buckle frame.
2. Brief Description of Prior Art
It is well known for a seat belt buckle to include an electric switch which is actuated by insertion of a tongue plate. Such switches are used in conjunction with buzzers or other warning devices which sound when an occupant of an automobile has not buckled his seat belt. One such switch is described in U.S. Pat. No. 4,608,469 issued to Gerald A. Doty on Aug. 26, 1986, wherein the switch components are encased to form a separate, modular assembly which can be inserted in a variety of different seat belt buckles. A channelway extending from the encasing outer closure guides a reciprocating plunger which moves back and forth in the channelway. The plunger is generally L-shaped, having a first upstanding leg which engages the tongue plate. The second leg of the plunger is received in the channelway and has a bottom surface which slides back and forth on a floor of the channelway. The second leg has a stairstep arrangement with a short vertical riser portion between two horizontal steps. This vertical riser portion engages a moveable switch contact which comprises one arm of a coil spring. The step arrangement is necessary to prevent the spring arm from sliding under the plunger during switch actuation.
While having been met with general acceptance in the automotive industry, several improvements could be realized. The arrangement of U.S. Pat. No. 4,608,469 provided flexibility of use (owing to its modular drop-in design) but did not directly sense internal conditions of the seat belt buckle. That is, the switch was actuated solely by insertion of the tongue plate, and did not reflect a locked or latched condition directly indicative of seat belt protection where the tongue plate is not only fully inserted and latched by a pawl, but the pawl itself is locked against opening.
As indicated above, the switch of U.S. Pat. No. 4,608,469 does not respond directly to an operating condition of the seat belt buckle, but responds only to an insertion of a tongue plate. In general, it is desirable to ensure that a switch be operated only in response to the intended buckle operating condition. For instance, operation of the switch could be improved if a signal generated by the switch contacts were made to respond solely to the proper positioning of a mating tongue plate of particular configuration, rather than some other member introduced into the buckle. Further improvements could result if the switch were made to respond directly to a movement of a locking mechanism which takes place only when the tongue plate is locked to the buckle frame.
As described, the switch of U.S. Pat. No. 4,608,469 is adapted for use with a so-called "top-release" buckle where the push button for unlatching the buckle is operated in a direction transverse to the direction of tongue plate insertion. Frequently, especially in foreign markets, a "side-release" buckle is employed, where the push button for buckle release is operated in a direction parallel to that of the tongue plate insertion. Buckles of this type, to which embodiments of the present invention are directed, employ a lock pin or latch bar which is positioned to block release of a latching pawl from locking engagement with a tongue plate until the push button is operated. Usually, the lock pin or bar is mounted to slide in slots in the frame and is shifted by movement of the push button from a blocking position (blocking the latch pawl) to a release position (in which the latch pawl is free to pivot away from latching engagement with the tongue plate). In such buckles, the push button is typically biased toward an outer position and is pushed inward to unblock and open the latch mechanism.
One example of this type of seat belt buckle is given in copending U.S. patent application Ser. No. 045,954 filed May 1, 1987 entitled "Improved Seat Belt Buckle." The application discloses a seat belt buckle having a buckle frame and a pivotal latching member mounted therein which includes an improved actuating system for locking the latching member and for assisting in ejecting a tongue plate from the frame when the latch mechanism is in its open position. The actuating system includes a stirrup-like linkage having a cylindrical ejector portion with ends joined between a pair of pivotally mounted arms. A locking cylinder for locking the latching member also extends between the arms for travel in conjunction with the ejector portion. A generally U-shaped retainer includes flat plate-like walls which are pinned to the pair of arms. The ejector portion is snap-locked into a slider member for sliding reciprocation therewith during seat belt buckle operations. The slider member includes a sliding rail which reciprocates back and forth in the buckle frame.
The above-described seat belt buckle could be improved by providing a compact, lightweight reliable electrical switch which detects the insertion of a tongue plate into the buckle frame and which directly responds to a latching of the tongue plate as well as a locking of the latch member. In addition to low assembly and production costs, a commercially practical switch should be capable of operation over a period of several years without maintenance, while being subjected to such adverse environmental factors as dust, temperature extremes, and excessive humidity. In particular, the contacts of the switch, to meet automotive manufacturers' specifications, must be satisfactorily cycled thousands of times. A simple arrangement for wiping the contacts of the switch would help ensure reliable operation over several years of use.